Streptococcus agalactiae are Gram positive polysaccharide encapsulated organisms that are also known as group B streptococcus (GBS). They are a common commensal of the human gastrointestinal and genital tract and also a cause of serious disease in infants and older adults (Baker, C. J., Vaccine, 31(Suppl. 4):D3-D6 (2013)). The main risk factor for GBS infection in infants is maternal colonization (Dillon, H. C., et al., J. Pediatr., 110(1):31-36 (1987)). As much as one in four women carry GBS recto-vaginally, which can infect the amniotic fluid or baby before or during delivery causing sepsis, pneumonia, and meningitis (Baker 2013; Heath, P. T., et al., BMJ Clin. Evid. (Online), pii:0323 (2014)). Twenty five percent of infants who survive GBS meningitis suffer from neurologic impairment with 19% experiencing cognitive delay, cerebral palsy, blindness, and hearing loss (Libster, R., et al., Pediatrics, 130(1):e8-152012 (2012)). GBS can also cause miscarriages and preterm deliveries and is linked to stillbirths (McDonald, H. M., et al., Infectious Diseases in Obstetrics and Gynecology, 8(5-6):220-227 (2000); Randis, T. M., et al., The Journal of Infectious Diseases, 210(2):265-273 (2014): Kessous, R., et al., J. Matern. Fetal Neonatal Med., 25(10):1983-1986 (2012)). Very low birth weight infants are at much higher risk of infection, with up to 3% infected and mortality rates of up to 30%, even with immediate antibiotic treatment (Heath 2014).
The introduction in the late 1990's of GBS screening and intrapartum antibiotic prophylaxis (IAP) in the U.S. demonstrated reduced rates of neonatal disease occurring within the first week of life (early onset disease [EOD]), but has had no measurable impact on rates of late onset disease (LOD) appearing thereafter within the first 3 months of life. U.S. rates of EOD and LOD cases are currently 0.25 and 0.27 per 1,000 births respectively (Centers for Disease Control and Prevention (CDC), Active Bacterial Core (ABC) Surveillance Report (2013) available at http://www.cdc.gov/abcs/reports-findings/survreports/gbs13.pdf). Following introduction of pneumococcal conjugate vaccines for prevention of invasive pneumococcal disease, including bacteremia and meningitis, and in spite of IAP for prevention of GBS disease, GBS has become the single most common cause of neonatal sepsis (EOD) and meningitis (<2 mo) in infants in the U.S. (Verani, J. R., et al., MMWR, 59(RR10):1-32 (2010); Thigpen, M. C., et al., New England Journal of Medicine, 364(21):2016-2025 (2011)). Unlike in the U.S., the introduction of prevention guidelines for invasive GBS disease and IAP has not reduced the incidence of EOD in the Netherlands or the U.K. (Bekker, V., et al., The Lancet Infectious Diseases, 14(11):1083-1089 (2014); Lamagni, T. L., et al., Clin. Infect. Dis., 57(5):682-688 (2013)). This lack of effect may be due to the lack of universal screening and restricting IAP to mothers in the highest risk groups (e.g., fever, prolonged ruptured membranes). Rates of EOD are significantly higher in countries that do not use IAP, with a mean incidence reported of 0.75 per 1,000 live births (95% CI 0.58-0.89) (Edmond, K. M, et al., Lancet, 379(9815):547-556 (2012)).
Another population at risk for GBS disease is the elderly. Risk factors include chronic medical problems such diabetes mellitus, cancer, heart failure, neurologic, and urologic conditions. According to CDC ABC surveillance data, the annual U.S. incidence of invasive GBS in 2013 was 0.28/1,000 adults or 12,400 cases/year in adults ≥65 years of age. This rate approaches the incidence of invasive pneumococcal disease in the elderly (vs. 0.30/1,000 for >65). These rates are expected to continue to increase in both the U.S. and in Europe (CDC 2013; Lamagni 2013).
One approach to prevent GBS disease among infants and the elderly is the use of a polysaccharide-based vaccine. The implementation of a maternal GBS prophylactic vaccine has the potential to prevent GBS disease among infants in the U.S., regardless of whether IAP is used. Although polysaccharides can be immunogenic on their own, conjugation of polysaccharides to protein carriers has been used to improve immunogenicity, particularly in infants and the elderly. Polysaccharide-protein conjugate vaccines are made using polysaccharides, generally from the surface coat of bacteria, linked to protein carriers. The chemical bonding of the polysaccharide and protein carrier induces an immune response against bacteria displaying the polysaccharide contained within the vaccine on their surface, thus preventing disease. Accordingly, vaccination using polysaccharides from pathogenic bacteria is a potential strategy for boosting host immunity.
The polysaccharides that cover bacteria vary greatly, even within a single species of bacteria. For example, in GBS there are ten different serotypes due to variation in the bacterial polysaccharide capsule. Therefore, it is desirable for polysaccharide-based vaccines to consist of a panel of polysaccharides to ensure breadth of coverage against different circulating strains.
The carrier protein can be either a related protein antigen from the target pathogen, boosting the specific immune response to that pathogen, or a generally immunogenic protein that serves more as an adjuvant or general immune response stimulant.
Individual monovalent polysaccharide-protein conjugates of GBS serotypes Ia, Ib, II, III, and V have been evaluated in phase 1 and 2 clinical trials in non-pregnant adults (Brigtsen, A. K., et al., Journal of Infectious Diseases, 185(9):1277-1284 (2002); Baker, C. J., et al., J. Infect. Dis., 188(1):66-73 (2003); Baker, C. J., et al., J. Infect. Dis., 189(6):1103-1112 (2004); Baker, C. J., et al., Vaccine, 25(1):55-63 (2007)). Bivalent II-TT and III-TT glycoconjugate vaccines and a trivalent vaccine comprising Ia-CRM197, Ib-CRM197 and III-CRM197 glycoconjugates have also been studied (Baker JID 2003; Clicaltrials.gov NCT01193920, NCT01412801, and NCT01446289). However, no GBS vaccines have yet to be approved.
Moreover, while the tri-valent vaccine covers >90% of invasive strains causing neonatal disease in South Africa (Madzivhandila, M., et al., PloS One, 6(3):e17861 (2011)), these same serotypes represent only 62% and 66% of invasive isolates in North America and Europe, respectively, based on surveillance of recent neonatal isolates from a global collection of 901 samples collected between 2004-2013 from the Tigecycline Evaluation and Surveillance Trial (T.E.S.T., http://www.testsurveillance.com/).
Analysis of the strains obtained from the T.E.S.T. samples showed that 95% of the strains collected belonged to one of the five documented major serotypes (Ia, Ib, II, III, and V) and a further 3% were serotype IV. A series of publications have also confirmed the appearance of serotype IV over the last decade in the Americas and in Europe (Diedrick, M. J., et al., J. Clin. Microbiol., 48(9):3100-3104 (2010); Teatero (2014); Meehan, M. et al., European Journal of Clinical Microbiology & Infectious Diseases, 33(7):1155-1162 (2014); Florindo, C., et al., Euro Surveillance: Bulletin European sur les Maladies Transmissibles (European Communicable Disease Bulletin), 19(23) (2014); Palmiero, J. K., et al., Journal of Clinical Microbiology, 48(12):4397-4403 (2010)). A study surveying recto/vaginal carriage in adults, which is a risk factor for transmission of GBS to the infant, also found 97% of isolates belonging to one of these six serotypes, with serotype IV representing a frequency of ˜4%. The study was designed to monitor carriage of beta-hemolytic streptococci (which includes GBS), Clostridium difficile, and Staphylococcus aureus in healthy U.S. adults (see Matson, M. A., et al, ICAAC, Abstract I-306 (Washington, D.C., Sep. 5-9, 2014)).
Similarly, analysis of T.E.S.T. samples showed 98% of U.S. blood isolates from older adults ≥65 years of age belong to the same six predominant serogroups. The most noticeable difference between the elderly isolates and the other populations is the serogroup distribution. For the isolates from elderly patients, serotype V strains constitute the largest group (34% vs. 18% for neonatal or 18% for adult carriage strains).
Other studies have found that there is a geographic variance of serotype prevalence. For instance, serotype VI and VIII isolates have been shown to be predominant colonizers of healthy pregnant women in Japan (Lachenauer, C. S., et al., JID 179(4):1030-1033 (1999).
Accordingly, a need exists for polysaccharide-protein conjugate vaccines or monoclonal antibodies to confer passive immunity as a means to prevent or treat GBS diseases, including those caused by emerging serotype IV, among broad populations worldwide.